This invention relates to a device for reducing splash and spray thrown from the wheels of a vehicle moving on wet pavement. More particularly this invention relates to a laminated spray-suppression device of thermoplastic material having a three-dimensional molded surface.
As disclosed in U.S. Pat. No. 3,899,192, incorporated herein by reference, laminated spray-suppression devices for mounting to the rear of the wheels of a moving vehicle are known in the prior art. In that patent a grass-like layer is shown facing the rotating wheel and this has been proven especially effective in absorbing impinging spray from a wet roadway surface and allowing it to drain back onto the pavement.
While the splash and spray reducing device comprising such a three-dimensional laminate has found wide acceptance in the transportation industry, this device is not completely free of drawbacks. Materials normally used to form three-dimensional layer of this laminate, such as low density polyethylene (LDPE), typically have poor low temperature mechanical properties, particularly ductility and impact. Cracking and resultant failure of these three-dimensional laminates due to poor low temperature ductility and impact resistance is often exacerbated by the geometry of the three-dimensional layer. This three-dimensional layer typically comprises a base portion in the form of a series of parallel rows of ribs and a plurality of blade-like protrusions extending from cup-like bases located between the parallel rows of ribs clustered at the intersections. The intersecting points at which the cup-like bases and ribs are joined provide areas of high stress localization which can result in the development of localized cracks which can propagate through the thickness of the three-dimensional layer. While it might be suspected that the utilization of a substrate or backing layer made from material which has good low temperature properties, such as high density polyethylene, would compensate for the deficiencies of the three-dimensional layer and provide the laminate with acceptable ductility and impact resistance. It has been found that the three-dimensional laminates exhibit significant embrittlement related failure when used at low temperature conditions. The low temperature embrittlement of the LDPE three-dimensional layer causes the failure of the entire laminate at temperatures at which the substrate itself remains ductile. The failure of the entire laminate is believed to be due to cracks which initiate in the LDPE three-dimensional layer, as described above, and which propagate through the entire thickness of the laminate. Propagation across the interface between the ductile backing layer and the brittle LDPE three-dimensional layer occurs where the bonding process produces strong association of the two layers.
As disclosed in U.S. Pat. No. 4,361,606, irradiation of the composite overcomes the problem and provides the device having a three-dimensional layer of LDPE with the desired balance of low temperature properties. However, irradiation has its deficiencies. More specifically, rather high dosages are necessary to alleviate cracking and this represents significant expense. Moreover, such dose levels provide an undesirable yellow tinge to the laminated product, e.g. to the backing which is often desired to be white. In addition catalysis residues, e.g. free radicals, may be developed in the various layers of polyethylene by the irradiation and react over long term periods to cause deterioration in the very properties intended to be enhanced. An alternative solution to the problem is disclosed in U.S. Pat. No. 4,391,870 where an intervening layer of a non-woven fabric core encapsulated on each side with an adhesive layer is located between the backing layer and the LDPE three-dimensional grass-like layer. Such encapsulated fabric core layer positioned between the backing layer and the LDPE three-dimensional grass-like layer serves to absorb and dissipate the energy of a crack as it is transmitted in low temperature service to such core layer from the embrittled LDPE layer thereby preventing the crack from propagating through to the backing layer. The use of such encapsulated fabric core layer however has its disadvantages. Specifically the use of such core layer requires additional material and manufacturing costs adversely effecting the economic viability of such spray-suppression devices.